Processes and apparatuses for drying coated moving webs of material are known to those skilled in the art. Thus, e.g., U.S. Pat. Nos. 4,936,025, 5,009,016, and 5,261,166 describe some illustrative prior art processes.
As is disclosed in U.S. Pat. No. 4,936,025, paper webs are coated by means of either separate coating devices, and/or by means of on-machine devices integrated in paper machines, and/or by means of surface-sizing devices (see lines 29-37 of column 1).
Attempts have repeatedly been made to increase the efficiency of the devices for drying coated paper webs. Thus, as is disclosed at lines 36-38 of U.S. Pat. No. 5,261,166, "Various attempts have been made in the prior art for decreasing the length and/or increasing the efficiency and line speed of such dryers." These attempts have not been entirely successful.
The efficiency of a drying system can be calculated by determining the number of pounds of water actually evaporated from the moving web. The theoretical amount of energy required to remove such amount of water can be calculated and then divided into the actual amount of energy consumed in the process. The ratio, times 100, is the percent efficiency of the process.
With present commercially available systems, the maximum drying efficiency obtained with moving coated paper webs is generally less than 50 percent. Furthermore, even with this relatively low efficiency, quality problems with the dried web often appear. Thus, the dried coated paper webs often demonstrate print mottle and other problems which frequently are caused by poor adhesion of the coating to the substrate.
It is an object of this invention to provide a process for drying a moving coated web of material which is substantially more efficient than prior art processes.
It is another object of this invention to provide a process for drying a moving coated web of material which, at an efficiency greater than 75 percent, produces a dried coated web of acceptable quality.
It is yet another object of this invention to provide a novel drying apparatus.